Popular smoking articles, such as cigarettes, have a substantially cylindrical rod-shaped structure and include a charge, roll or column of smokable material, such as shredded tobacco (e.g., in cut filler form), surrounded by a paper wrapper, thereby forming a so-called “smokable rod” or “tobacco rod.” Normally, a cigarette has a cylindrical filter element aligned in an end-to-end relationship with the tobacco rod. Typically, a filter element comprises plasticized cellulose acetate tow circumscribed by a paper material known as “plug wrap.” Certain filter elements can incorporate polyhydric alcohols. Typically, the filter element is attached to one end of the tobacco rod using a circumscribing wrapping material known as “tipping paper.” It also has become desirable to perforate the tipping material and plug wrap, in order to provide dilution of drawn mainstream smoke with ambient air. Descriptions of cigarettes and the various components thereof are set forth in Tobacco Production, Chemistry and Technology, Davis et al. (Eds.) (1999). A cigarette is employed by a smoker by lighting one end thereof and burning the tobacco rod. The smoker then receives mainstream smoke into his/her mouth by drawing on the opposite end (e.g., the filter end) of the cigarette.
The discarded portion of the cigarette rod is primarily composed of the filter element, which typically consists of tightly-compacted and highly crimped cellulose acetate fibers bonded at their contact points and wrapped by the plug wrap and tipping paper. The presence of the wrapping materials, the fiber-to-fiber bonding, and the compacted nature of conventional filter elements has a detrimental effect on the rate of degradation of cigarette filters in the environment. Unless the filter element is unwrapped and the fibers spread apart to increase exposure, biodegradation of the filter can take several years.
A number of approaches have been used in the art to promote an increased rate of degradation of filter elements. One approach involves incorporation of additives (e.g., water soluble cellulose materials, water soluble fiber bonding agents, photoactive pigments, degradable starch particles, or phosphoric acid) into the cellulose acetate material in order to accelerate polymer decomposition. See U.S. Pat. No. 5,913,311 to Ito et al.; U.S. Pat. No. 5,947,126 to Wilson et al.; U.S. Pat. No. 5,970,988 to Buchanan et al.; and U.S. Pat. No. 6,571,802 to Yamashita; and US Pat. Appl. Publication No. 2011/0036366 to Sebastian. Incorporation of slits into a filter element has been proposed for enhancing biodegradability, such as described in U.S. Pat. No. 5,947,126 to Wilson et al. and U.S. Pat. No. 7,435,208 to Garthaffner. U.S. Pat. No. 5,453,144 to Kauffman et al. describes use of a water sensitive hot melt adhesive to adhere the plug wrap in order to enhance biodegradability of the filter element upon exposure to water. U.S. Pat. No. 6,344,349 to Asai et al. proposes to replace conventional cellulose acetate filter elements with a filter element comprising a core of a fibrous or particulate cellulose material coated with a cellulose ester to enhance biodegradability.
In some cases, conventional cellulose acetate has been replaced with other materials, such as moisture disintegrative sheet materials, extruded starch materials, or polyvinyl alcohol. See U.S. Pat. No. 5,709,227 to Arzonico et al; U.S. Pat. No. 5,911,224 to Berger; U.S. Pat. No. 6,062,228 to Loercks et al.; and U.S. Pat. No. 6,595,217 to Case et al. U.S. application Ser. No. 12/827,618, filed Jun. 30, 2010, suggests the use of certain biodegradable polymers, such as polylactic acid, in a filter element for a cigarette. Formation of a cigarette filter using biodegradable polymers can be challenging because conventional plasticizers used in combination with cellulose acetate fibers are often poorly suited to plasticize other types of polymers.
Accordingly, there remains a need in the art for a smoking article filter exhibiting enhanced environmental degradation properties, particularly where the filter can be manufactured with only minor modification of conventional filter rod production equipment.